Release agents have been applied to equipment such as press platens used in molding/pressing lignocellulosic materials, casting concrete and molding polymer foams. The release agents are used to aid the removal of articles produced from manufacturing equipment. Examples of release agents include oils, wax, polishes, metallic salts, silicones and polytetrafluoroethylene. Many of the current release agents either contain EDTA or have EDTA added prior to their use to control specific water problems such as mineral deposits. However, the problem is that in these very high temperature environments, the addition of EDTA will exacerbate the already very corrosive atmosphere.
The following patents are representative of the art of release agents:    U.S. Pat. No. 4,257,995 issued to McLaughlin et al.;    U.S. Pat. No. 4,257,996 issued to Farrissey, Jr. et al. on Mar. 24, 1981;    U.S. Pat. No. 4,609,570 issued to Couleau et al. on Sep. 3, 1986;    U.S. Pat. No. 5,908,496 issued to Singule et al. on Jun. 1, 1999;    U.S. Pat. No. 5,194,584 issued to Leahy on Mar. 16, 1993;    U.S. Pat. No. 5,942,058, issued to Sleeter et al. on Aug. 24, 1999;    U.S. Pat. No. 6,132,503 issued to Singule et al. on Oct. 17, 2000;    U.S. Pat. No. 6,231,656 issued to Dekerf et al. on May 15, 2001;    EP 46014, and    EP 57502.
Release agents are especially useful in the engineered wood industry when molding lignocellulosic materials such as wood sheets, wood chips, wood fibers, wood flakes, wood strands, wood shavings, wood veneers, wood wool, cork, tree bark, sawdust, paper straw, flax, hulls, seeds, and nutshells. etc., into composite structures with adhesives. There may be added to these lignocellulosic materials other particulate or fibrous material in an amount of up to 25 wt %. These include mineral fillers, glass fibers, rubber, plastic fibers, or particles.
Examples of composite products comprised of lignocellulosic materials include: particle board, oriented strand board (OSB), plywood, chip board, medium density fiber board (MDF), hardboard, Agricultural board, and structural strand lumber.
An example of an OSB industry manufacturing process is as follows. Wood chips (wafers) are mixed with slurry of various waxes, thermosetting adhesives (such as phenolic resins and/or MDI) and other chemicals. This wood chip and slurry mixture is formatted into a continuous mat of various thicknesses (depending on the desired final 4×8 panel thickness). The web is sprayed with a release agent made up of various types of chemicals in an aqueous solution. This web is then cut into pieces, e.g., 24×8 Ft. pieces, or fed continuously into a press section where the web mat is pressed into boards or panels of desired thickness at pressures typically from 2 to 6 MPa and temperatures from 375 to 500 degrees Fahrenheit. The presses are made up of top and bottom platens, primarily mild steel that press the mat into the desired thickness under both heat and pressure which “cures” these thermosetting resin compounds. These techniques and conditions are modified as needed.
The engineered wood industry has been plagued with corrosive problems on the platens (in the press section) in preparing these products in that conventional processes create a highly corrosive atmosphere during manufacture. For example, the process described above can be very corrosive depending on the chemical attributes of the water, the water oxygen content, corrosive chemistries (such as carbonic acid, oxygen, and EDTA) introduced in the process, and the amount of oxygen released during the pressing process. When the web is subjected to this extreme heat and pressure, the dissolved oxygen is liberated from the water and it will attack the mild steel platens, commonly called “oxygen pitting” of the metal. This release of oxygen at high temperatures exacerbates corrosion by the presence of EDTA which is a component of all commercially available release agents at the time of the provisional filing of this patent.
Different types of chemical analysis can provide valuable information in corrosion monitoring programs. The measurement of pH, conductivity, dissolved oxygen, metallic and other ion concentrations, water alkalinity, concentration of suspended solids, inhibitor concentrations and scaling indices all fall within this domain. Several of these measurements can be made on-line using appropriate sensors.
The corrosive nature of the water (or any fluid) can be predicted by using the generally accepted criteria found in models such as the “Ryznar” or “Langolier” indexes.
The Ryznar stability index (RSI) attempts to correlate an empirical database of scale thickness observed in municipal water systems to the water chemistry. Like the LSI, the RSI has its basis in the concept of saturation level. Ryznar attempted to quantify the relationship between calcium carbonate saturation state and scale formation. The Ryznar index takes the form:RSI=2(pHs)−pH
Where:                pH is the measured water pH        pHs is the pH at saturation in calcite or calcium carbonate.        
The empirical correlation of the Ryznar stability index can be summarized as follows:                RSI<<6 the scale tendency increases as the index decreases        RSI>> the calcium carbonate formation probably does not lead to a protective corrosion inhibitor film        RSI>>8 mild steel corrosion becomes an increasing problem.        
The actual corrosion rate of any given fluid on metal surfaces can be measured, quantified, and predicted by using the generally accepted methods of measuring weight loss on metal “coupons” over a specified period of time. These methods have been incorporated in a wide range of industries to quantify, compare, and predict the chemical and physical conditions of a process on metal equipment.
The terms below have the following meaning when used herein.
A “film formed by a metal passivator” is one produced by chemical action, with or without electrical assistance. The treatments change the immediate surface layer of metal into a film of metallic oxide or other compound which has better corrosion resistance than the natural oxide film and provides an effective base or key for supplementary protection such as paints. In some instances, these treatments can also be a preparatory step prior to painting.
An “inhibitor” is a chemical substance or combination of substances that, when present in the proper concentration and form in the environment prevents or reduces corrosion.
“Internal Oxidation” is the formation of isolated particles of corrosion products beneath the metal surface. This occurs as the result of preferential oxidation of certain alloy constituents by inward diffusion of oxygen, nitrogen, sulfur, etc.
“Chemical conversion Coating” is a protective or decorative nonmetallic coating produced in situ by chemical reaction of a metal with a chosen environment. It is often used to prepare the surface prior to the application of an organic coating.
“Reactive Metal” is a metal that readily combines with oxygen at elevated temperatures to form very stable oxides, for example, titanium, zirconium, and beryllium.
“Corrosion” is a chemical (often electrochemical) process that destroys structural materials. Typically it refers to corrosion of metals, but any other material (e.g., plastic or semiconductor) will also corrode. The simplest example of metallic corrosion is the rusting of iron in air. Iron is spontaneously oxidized by the oxygen in air to iron oxides (while the oxygen is being reduced). Metallic corrosion is very often an electrochemical process. It is always electrochemical when the metal is immersed in a solution, but even in atmospheric corrosion a thin film of condensed moisture often covers the surface. The metal in the corrosive solution essentially acts as a short-circuited galvanic cell. Different areas of the surface act as anode and cathode, at the anodic areas the metal is oxidized to an oxide while at the cathodic areas the dissolved oxygen is being reduced. The spontaneous complementary oxidation/reduction processes of “rusting” are spatially separated while an electrical current is flowing “internally” from one part of the corroding metal to another; the current is totally “wasted” as it produces no useful work but only generates heat. (A cell arrangement like this is often called a “local cell.”) Corrosion products are typically oxides, but other products (e.g., sulfides) can also form depending on the environment. Corrosion always involves oxidation of the corroding material in the general sense of the term.
“Passivating inhibitors” (passivators) are compounds that cause a large anodic shift of the corrosion potential, forcing the metallic surface into the passivation range. There are two types of passivating inhibitors: Oxidizing anions, such as chromate, nitrite and nitrate that can passivate steel in the absence of oxygen and Non oxidizing ions such as phosphate, tungstate and molybdate that require the presence of oxygen to passivate steel. These inhibitors are the most effective and consequently the most widely used. Chromate based inhibitors are the least expensive inhibitors and were used until recently in a variety of applications, e.g. recirculation-cooling systems of internal combustion engines, rectifiers, refrigeration units, and cooling towers. Sodium chromate, typically in concentrations of 0.04-0.1% was used for these applications. At higher temperatures or in freshwater with chloride concentrations above 10 ppm higher concentrations are required. If necessary, sodium hydroxide is added to adjust the pH to a range of 7.5-9.5. If the concentration of chromate falls below a concentration of 0.016% corrosion will be accelerated. Therefore it is essential that periodic colorimetric analysis be conducted to prevent this from occurring. In general, passivation inhibitors can actually cause pitting and accelerate corrosion when concentrations fall below minimum limits. For this reason it is essential that monitoring of the inhibitor concentration be performed.
The simplest, and longest-established, method of estimating corrosion losses in plant and equipment is weight loss analysis. A weighed sample (coupon) of the metal or alloy under consideration is introduced into the process, and later removed after a reasonable time interval (usually 30, 60 or 90 days) The coupon is then cleaned of all corrosion products and is reweighed. The weight loss is converted to a total thickness loss, or average corrosion rate using proper conversion equations.
Weight loss determination has a number of attractive features that account for its sustained popularity. It is:                Simple: No sophisticated instrumentation is required to obtain a result.        Direct: A direct measurement is obtained, with no theoretical assumptions or approximations.        Versatile: It is applicable to all corrosive environments, and gives information on all forms of corrosion.        
The choice of technique for initial preparation of the coupon surface, and for cleaning the coupon after use, is critical in obtaining useful data. Both the relevance and reproducibility of weight loss data are highly sensitive to the inherent suitability of these techniques, and to the care with which they are executed.
Surface finishing methods vary across a broad range for specific applications. Blasting with glass bead, sand, or other aggregate can provide an acceptable finish for some applications. Sanding with abrasive belts, or surface or double disc grinding with abrasive stones also provides an excellent surface for evaluation. Cleaning of specimens before weighing and exposure is critical to remove any contaminants that could affect test results. NACE Recommended Practice RP-0775 and ASTM G-1 G-4 are incorporated herein by reference for further detail on surface finishing and cleaning of weight-loss coupons.